This invention relates to cutting threads into short sections, particularly threads in the form of rovings of untwisted or slightly twisted strands of a mineral substance such as glass fibers.
Short pieces of glass fiber rovings, usually in lengths between 3 to 12 millimeters have been found to be useful as a reinforcement material in synthetic polymeric resins which are cast or molded into complex shapes. Rovings possess relatively little cohesion, and as a consequence, the individual strands of which they are constituted tend to separate during the cutting operation in which the pieces are cut from a continuous length of roving. This results in the formation of a considerable quantity of waste material in the form of fibers and particles which, as the cutting operation proceeds, tends to fill and to be packed into the spaces between cutting blades carried by a rotating cutting drum. This tends to make the cutting process faulty and can result in waste material being introduced into the cuttings.
It has been known to cut rovings into short lengths by the use of a rotating drum having radially extending cutting blades, which drum acts in conjunction with a rotating support drum, the rovings being carried on the support drum and being cut by the blades as the blades come into contact with the surface of the support drum.
One type of roving cutting apparatus employing means for ejecting the cut pieces from between adjacent cutting blades is shown in U.S. Pat. No. 3,555,947. In devices of the type illustrated in the aforementioned patent, a drum formed of a plurality of ejecting bars is mounted for rotation eccentrically with respect to the axis of rotation of the drum to which the cutting blades are attached. In certain apparatus of the type generally shown in the mentioned patent, guides are utilized for guiding the movement of the ejecting bars between the cutting blades. A drawback of this apparatus is that the fibrous wastes resulting from the cutting operation become lodged in the guides that are located between the ejection bars and the cutting blades. As a result of metal-to-metal contact as the ejecting bars move in their guides, a black powder is produced, which falls into the finished cuttings and thus renders the cuttings unmarketable. Moreover, the metal-to-metal contact of the ejecting bars and the guides over a period of time, results in wear of the various parts, necessitating their replacement. In addition, during operation, this apparatus has a very high noise output level, which is an important factor with respect to worker fatigue. Finally, the friction developed by the metal-to-metal mounting of the components and the high noise level of the apparatus limits its speed of rotation and, consequently, its production capacity.
Certain other arrangements for cutting rovings and employing drums having ejector elements for urging cuttings from spaces between cutting blades are shown in Applicant's U.S. Pat. Nos. 3,942,401 and 3,945,280. In these arrangements, the ejector elements comprise flexible bars that are secured at each of their ends to the cutting drum, the central portions of the ejector bars being free to move radially with respect to the axis of rotation of the cutting drum in the spaces between adjacent blades.